Patent GB-1534936-A (GB)
Title: Method and a device for measuring the sparking efficiency in electrical discharge machining
IPC: B23H1/02
Filed: 1976-03-31
Abstract: 1534936 Electro erosion ATELIERS DES CHARMILLES SA 31 March 1976 [11 April 1975] 12894/76 Heading B3V Sparking efficiency between an electrode 1 and a workpiece 2 is measured by detecting whenever a discharge is erosive and driving an electrical quantity of value proportional to the duration of all the erosive discharges produced during a defined period of machining. As shown a D.C. source S is connected in series with a power switch, e.g. transistor 4, and a resistor R. A voltage taken across R at every machining pulse is delivered to a Schmitt trigger 6 connected to a flip-flop T A  piloting a flip-flop T B . The output of flip-flop T B  controls the switch 4 via an inverter 5. The trigger and flip-flop arrangement enables discharges of constant duration separated by intervals of constant duration to be achieved under the control of the circuit including the switch 4 provided a switch J 1  is in the position shown; independently if the switch J 1  connects the inverter to the flipflop T A . A device 7 detects short circuits, arcs or pollution and signals them to an AND gate 2 of a display unit 45 via a NOR gate 11. The output signal of the trigger 6 is also applied to the gate 12. An output pulse from gate 12 thus indicates that an effective discharge is taking place and lasts throughout the discharge, the gate 11 closing the gate 12 if the detector 7 signals an undesirable machining condition. The output signal from gate 12 is applied to a circuit 13 which calculates its mean value over a predetermined period and passes a corresponding analog signal to a frequency converter 14. The output of the converter is passed to a frequency meter F M  via a circuit 15 only, in which the frequency is multiplied by a number N1 representing the level of the discharge current, or via a circuit 16 also in which the frequency is multiplied by a number N r  representing the theoretical removal of material per unit of time and current. The meter F M  thus indicates a value corresponding to a characteristic value of either the useful machining current or the real rate of erosion. A first alternative display unit 48, Fig. 4, is for use with an erosion circuit without a switch J 1  so that the flip-flop T A  fixes the duration of each erosive discharge The detection device gives a signal for every effective discharge to a terminal A connected to a counter 24 which adds pulses during a period fixed by a clock 25 which also acts on amemory 26 which stores pulses from counter 24 during that period. In multiplying circuits 27, 28, 29, the output of memory 26 is multiplied by a number N TA , representing the duration of each discharge as fixed by the flip-flop TA, and the numbers N 1  and N r . The output of circuits 28 or 29, depending on the position of switch J 2 , is applied to a numerical display device AN. Figures 2, 3 or 5 relate to further display units including volt or frequency meters. The electrical quantity displayed in the units may be used to pilot a circuit for varying machining conditions.